Amine-initiated elastomers having hysteresis reducing interaction with silica

ABSTRACT

The reduction of hysteresis in a silica-filled, vulcanized elastomeric compound is produced by mixing diene monomer and optionally monovinyl aromatic monomer with a lithium amine initiator and, optionally, a modifier; effecting polymerization conditions; terminating polymerization with an amino group producing terminator to form an amine functionalized diene elastomer; compounding the amine functionalized diene elastomer with an amorphous silica filler and a vulcanization agent; and, effecting vulcanization. A pneumatic tire tread stock incorporating the vulcanized elastomer compound exhibits decreased rolling resistance in the tire.

TECHNICAL FIELD

The subject invention relates to the anionic polymerization of silicafilled diene polymer and copolymer elastomers. More specifically, thepresent invention relates to anionic polymerization employing lithiumamine initiator and various terminator compounds providing improveddispersion of silica in elastomeric compounds.

Silica-filled compounds which include these functional diene polymersand copolymers prepared according to the present invention, have reducedhysteresis characteristics. Articles such as tires, power belts and thelike which are prepared from these compounds exhibit increased rebound,decreased rolling resistance and less heat build-up during mechanicalstress operations.

BACKGROUND OF THE INVENTION

In the art it is desirable to produce elastomeric compounds exhibitingreduced hysteresis when properly compounded with other ingredients suchas reinforcing agents, followed by vulcanization. Such elastomers, whencompounded, fabricated and vulcanized into components for constructingarticles such as tires, power belts, and the like, will manifestproperties of increased rebound, decreased rolling resistance and lessheat-build up when subjected to mechanical stress during normal use.

The hysteresis of an elastomeric compound refers to the differencebetween the energy applied to deform an article made from theelastomeric compound and the energy released as the elastomeric compoundreturns to its initial, undeformed state. In pneumatic tires, loweredhysteresis properties are associated with reduced rolling resistance andheat build-up during operation of the tire. These properties, in turn,

In such contexts, the property of lowered hysteresis of compounded,vulcanizable elastomer compositions is particularly significant.Examples of such compounded elastomer systems are known to the art andare comprised of at least one elastomer (that is, a natural or syntheticpolymer exhibiting elastomeric properties, such as a rubber), areinforcing filler agent (such as finely divided carbon black, thermalblack, or mineral fillers such as clay and the like) and a vulcanizingsystem such as sulfur-containing vulcanizing (that is, curing) system.

Previous attempts at preparing reduced hysteresis products have focusedupon increased interaction between the elastomer and the compoundingmaterials such as carbon black, including high temperature mixing of thefiller-rubber mixtures in the presence of selectively-reactive promotersto promote compounding material reinforcement, surface oxidation of thecompounding materials, chemical modifications to the terminal end ofpolymers using 4,4'-bis(dimethylamino)benzophenone (Michler's ketone),tin coupling agents and the like and, surface grafting.

It has also been recognized that carbon black, employed as a reinforcingfiller in rubber compounds, should be well dispersed throughout therubber in order to improve various physical properties. One example ofthis recognition is provided in published European Pat. Appln. EP 0 316255 A2 which discloses a process for end capping polydienes by reactinga metal terminated polydiene with a capping agent such as a halogenatednitrile, a heterocyclic aromatic nitrogen-containing compound or analkyl benzoate. Additionally, the application discloses that both endsof the polydiene chains can be capped with polar groups by utilizingfunctionalized initiators, such as dialkylamino lithium compounds.However, results from such initiation show that no improvement inhysteresis is achieved when the elastomeric compositions are filled withcarbon black.

Various organolithium polymerization initiators are also known in theart. U.S. Pat. No. 3,439,049, owned by the Assignee of record, disclosesan organolithium initiator prepared from a halophenol in a hydrocarbonmedium.

U.S. Pat. No. 4,015,061 is directed toward amino-functional initiatorswhich polymerize diene monomers to form mono- or di-primary arylamine-terminated diene polymers upon acid hydrolysis. U.S. Pat. No.4,914,147 discloses terminal modifying agents includingdialkylamino-substituted aromatic vinyl compounds such asN,N'-dimethylamino benzophenone and p-dimethylamino styrene, in rubbercompositions having reduced hysteresis characteristics. In U.S. Pat. No.4,894,409, an amino group-containing monomer, such as2-N,N-dimethylaminostyrene is polymerized to form an aminogroup-containing diene based polymer.

Other patents owned by the assignee of record, directed toamine-containing polymerization initiators include U.S. Patent Nos.5,238,893; 5,274,106; 5,329,005; 5,332,810; 5,393,721; 5,496,940;5,519,086; 5,521,309; 5,523,371; and 5,552,473. Lawson, et al., inAnionic Polymerization of Dienes Using Homogeneous Lithium Amide (N-Li)Initiators, ACS Preprint, Polymer Division, 37 (2) 1996, at page 728,disclosed that, for carbon black-filled compounds, only cyclic aminolithium initiators of a certain size provided elastomeric compoundsexhibiting reduced hysteresis. The carbon black-filled elastomericcompounds containing aliphatic amino initiators did not reducehysteresis.

Precipitated silica has been increasingly used as a reinforcingparticulate filler in carbon black-filled rubber components of tires andmechanical goods. Silica-loaded rubber stocks, however, exhibitrelatively poor resilience and, thus, increased hysteresis.

The present invention provides initiators for anionic polymerizationwhich become incorporated into the elastomer chain, as well as variousterminators for the polymerization, and produce functional groups whichgreatly improve the dispersability of silica filler throughout theelastomeric composition during compounding. As will be describedhereinbelow, these initiators and terminators both contain amine groups.The initiator further contains a fugitive lithium moiety.

It has heretofore been unknown to utilize a combination of both amineproducing initiators and terminators to increase dispersion of silicafiller in diene polymer and copolymer elastomeric compounds, and tothereby reduce the hysteresis of the cured compounds.

SUMMARY OF INVENTION

It is therefore an object of the present invention to provide anionicpolymerization initiators and terminators which improve the dispersionof silica filler in diene polymer elastomers.

It is another object of the present invention to provide a method forreducing the hysteresis of silica-filled elastomeric vulcanizablecompounds.

It is another object of the present invention to provide vulcanizablesilica-filled elastomeric compounds, which upon vulcanization, exhibitreduced hysteresis.

It is still another object of the present invention to provide animproved pneumatic tire having decreased rolling resistance.

The foregoing objects, together with the advantages thereof over theexisting art, which shall become apparent from the specification whichfollows, are accomplished by the invention as hereinafter described andclaimed.

The present invention provides a process for the production ofdiene-based elastomeric compositions having reduced hysteresisproperties when compounded with silica filler and vulcanized, theprocess comprising mixing a diene monomer and optionally a monovinylaromatic monomer or a triene with a lithium amine initiator compoundoptionally in the presence of a modifier, wherein the lithium amineinitiator compound is selected from the group consisting of compounds ofthe formulas R'₂ N-Li and R'₂ N-R"-Li, wherein each R' is the same ordifferent and is a C₁₋₁₂ hydrocarbyl group and wherein R" is a divalenthydrocarbyl group of 2 to 20 carbons and the lithium atom is not bondedto a carbon which is directly bonded to the amine nitrogen effectingpolymerization conditions terminating polymerization with a terminatingagent to form a functionalized diene elastomer compounding thefunctionalized diene elastomer with an amorphous silica filler and avulcanization agent, and effecting vulcanization of the silica filled,functionalized diene filled elastomeric compound.

The present invention further provides a vulcanizable silica-filledcompound comprising a diene elastomer containing a lithium amineinitiator-derived functionality and a functionality derived from aterminator, a silica filler, and a vulcanization agent, wherein thelithium amine initiator-derived functionality is a residue of a lithiumamine initiator derived from a reaction of a secondary amine with ahydrocarbyl lithium and of the formula R'₂ N-Li, wherein each R' is thesame or different and is a C₁₋₁₂ hydrocarbyl group.

The present invention still further provides a vulcanizable silicafilled compound comprising a diene elastomer containing a lithium aminederived functionality and a functionality derived from a terminator, asilica filler, and a vulcanization agent, wherein the lithium aminederived functionality is a residue of a lithium-hydrocarbon substitutedtertiary amine of the formula R'₂ N-R"-Li, wherein each R' is the sameor different and is a C₁₋₁₂ hydrocarbyl group and wherein R" is adivalent hydrocarbyl group of 2 to 20 carbons and the lithium atom isnot bonded to a carbon which is directly bonded to the amine nitrogen.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In general, the present invention provides the obtainment of enhancedpolymer filler interactions with silica, thereby reducing hysteresis.This is done by the use of amino containing initiators (i.e., lithiumamine initiators) and, preferably, amino group producing terminators. By"amino group producing terminator" is meant a nitrogen containingprecursor compound which acts as a terminator for a "living" dienepolymer, and which after termination, contains or provides an aminogroup to form an amine functionalized diene elastomer. Such acombination of both amino containing initiators and amino groupproducing terminators has the advantage that the initiation will put areactive group on almost all of the polymer chains and then anyadditional end capping during termination will give polymers having anincreased level of reactivity towards silica filler when compared toconventionally initiated polymers modified only by termination.

The lithium amine initiators used in the present invention includelithium imides wherein a lithium atom is directly bonded to the nitrogenof a secondary amine or (lithium-hydrocarbyl) substituted amine whereinthe lithium atom is directly bonded to a carbon which is part of ahydrocarbyl group which, in turn, is bonded to a nitrogen.Representative of the former (i.e., lithium bonded to nitrogen) arecompounds of the structural formula R'₂ N-Li, and of the latter (i.e.,lithium bonded to a carbon), compounds of the structural formula R'₂N-R"-Li, wherein each R' in either formula is a monovalent hydrocarbylgroup, preferably having 1 to 12 carbons and R" is a divalenthydrocarbyl group, preferably having 2 to 20 carbons. More particularly,the R' in either of the formulas may be a C₁₋₁₂ hydrocarbyl group, suchas, for instance, a C₁₋₁₂ allyl group. In the latter formula, it will beappreciated that the lithium atom is preferably not bonded to a carbonwhich is directly bonded to the amine nitrogen, but rather, is separatedby at least one, and more preferably, at least 3 carbon atoms.

The lithium amine initiators according to the present invention, areemployed to prepare any anionically-polymerized elastomer, e.g.,polybutadiene, polyisoprene and the like, and copolymers thereof withmonovinyl aromatics such as styrene, alpha methyl styrene and the like,or trienes such as myrcene. Thus, the elastomers include dienehomopolymers, A, and copolymers thereof with monovinyl aromaticpolymers, B. Exemplary diene homopolymers are those prepared fromdiolefin monomers having from 4 to about 12 carbon atoms. Exemplaryvinyl aromatic polymers are those prepared from monomers having from 8to about 20 carbon atoms. Examples of conjugated diene monomers and thelike useful in the present invention include 1,3-butadiene, isoprene,1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and 1,3-hexadiene, andaromatic vinyl monomers include styrene, α-methylstyrene,p-methylstyrene, vinyltoluenes and vinylnaphtalenes. The conjugateddiene monomer and aromatic vinyl monomer are normally used at the weightratios of about 90/10 to about 55/45, preferably about 80/20 to about65/35.

Preferred elastomers include diene homopolymers such as polybutadieneand polyisoprene and copolymers such as styrene butadiene rubber (SBR).Copolymers can comprise from about 99 to 55 percent by weight of dieneunits and from about 1 to about 45 percent by weight of monovinylaromatic or triene units, totaling 100 percent. The polymers andcopolymers of the present invention may have the diene portion with a1,2-microstructure contents ranging from about 10 to about 80 percent,with the preferred polymers or copolymers having 1,2-microstructurecontents of from about 25 to 65 percent. The molecular weight of thepolymer that is produced according to the present invention, ispreferably such that a proton-quenched sample will exhibit a gum Mooneyviscosity (ML₄ /212° F.) of from about 10 to about 150. The copolymersare preferably random copolymers which result from simultaneouscopolymerization of the monomers, as is known in the art.

The lithium amine initiators of the present invention preferably include3-dimethylaminopropyllithium (i.e., (CH₃)₂ NCH₂ CH₂ CH₂ Li), and thelithium imides of dimethylamine, diethylamine, dipropylamine,dibutylamine, and the like. Lithium amines derived from more basic(pK_(b) of less than about 6) amines are preferred, in view of theacid-based interactions that occur with the silica filler. Such usefullithium amine initiators of both types are known as are described inU.S. Pat. Nos. 5,238,893; 5,274,106; 5,332,810; 5,491,230; 5,496,940;and 5,502,131, the disclosures of which are incorporated herein byreference.

Polymerization is usually conducted in a conventional solvent foranionic polymerizations such as the various cyclic and acyclic hexanes,heptanes, octanes, pentanes, their alkylated derivatives, and mixturesthereof, as well as aromatic solvents such as benzene, t-butylbenzene,toluene, and the like. Other techniques for polymerization, such assemi-batch and continuous polymerization may be employed. In order topromote randomization in copolymerization and to increase vinyl content,a modifier may optionally be added to the polymerization ingredients.Amounts range between 0 to 90 or more equivalents per equivalent oflithium. The amount depends upon the amount of vinyl desired, the levelof styrene employed and the temperature of the polymerizations, as wellas the nature of the specific polar coordinator (modifier) employed.

Compounds useful as modifiers are organic and include those having anoxygen or nitrogen hetero-atom and a non-bonded pair of electrons.Examples include dialkyl ethers of mono and oligo alkylene glycols;"crown" ethers; tertiary amines such as tetramethylethylene diamine(TMEDA); THF; THF oligomers; linear and cyclic oligomeric oxolanylalkanes, such as 2-2'-di(tetrahydrofuryl) propane, di-piperidyl ethane,hexamethylphosphoramide, N-N'-dimethylpiperazine, diazabicyclooctane,diethyl ether, tributylamine and the like. Details of linear and cyclicoligomeric oxolanyl modifiers can be found in U.S. Pat. No. 4,429,091,owned by the Assignee of record, the subject matter of which isincorporated herein by reference.

Polymerization is usually begun by charging a blend of the monomer(s)and solvent to a suitable reaction vessel, followed by the addition ofthe modifier and the initiator. Alternatively, the monomer and modifiercan be added to the initiator. The procedure is carried out underanhydrous, anaerobic conditions. The reactants are heated to atemperature of from about 10° to about 150° C. and are agitated forabout 0.1 to 24 hours. After polymerization is complete, the product isremoved from the heat and terminated in one or more ways.

To terminate the polymerization, a terminating agent, coupling agent orlinking agent may be employed, all of these agents being collectivelyreferred to herein as "terminating agents". Certain of these agents mayprovide the resulting polymer with a multifunctionality. That is, thepolymers initiated according to the present invention, carry at leastone amine functional group as discussed hereinabove, and may also carrya second functional group selected and derived from the group consistingof terminating agents, coupling agents and linking agents.

According to the present invention, useful terminating, coupling orlinking agents include an amino producing group, exemplified by but notlimited to the following: 4,4'-bis(dialkylamino)benzophenone (such as4,4'-(dimethylamino)benzophenone or the like);N,N-dialkylamino-benzaldehyde (such as dimethylaminobenzaldehyde or thelike); 1,3-dialkyl-2-imidazolidinones (such as1,3-dimethyl-2-imidazolidinone or the like); 1-alkyl substitutedpyrrolidinones; 1-aryl substituted pyrrolidinones; dialkyl- anddicycloalkyl-carbodiimides having from about 5 to about 20 carbon atoms;##STR1## wherein each R₂ is the same or different and is an alkyl,cycloalkyl or aryl, having from 1 to about 12 carbon atoms. For example,R₂ may include methyl, ethyl, nonyl, t-butyl, phenyl or the like.

R₃ is an alkyl, phenyl, alkylphenyl or dialkylaminophenyl, having from 1to about 20 carbon atoms. For example, R₃ may include t-butyl,2-methyl-4-pentene-2-yl, phenyl, p-tolyl, p-butylphenyl,p-dodecylphenyl, p-diethyl-aminophenyl, p-(pyrrolidino)phenyl, and thelike.

Each R₄ is the same or different, and is an alkyl or cycloalkyl havingfrom 1 to about 12 carbon atoms. Two of the R₄ groups may together forma cyclic group. For example, R₄ may include methyl, ethyl, octyl,tetramethylene, pentamethylene, cyclohexyl or the like.

R₅ may include alkyl, phenyl, alkylphenyl or dialkylaminophenyl, havingfrom 1 to about 20 carbon atoms. For example, R₅ may include methyl,butyl, phenyl, p-butylphenyl, p-nonylphenyl, p-dimethylaminophenyl,p-diethylaminophenyl, p-(piperidino)phenyl, or the like.

Other useful terminating agents may include those of the structuralformula (R₁)_(a) ZX_(b), wherein Z is tin or silicon. It is preferredthat, wherein Z is tin, then the terminating agent be (R₁)₃ SnX, whereR₁ is an alkyl having from about 1 to about 20 carbon atoms; acycloalkyl having from about 3 to about 20 carbon atoms; an aryl havingfrom about 6 to about 20 carbon atoms; or, an aralkyl having from about7 to about 20 carbon atoms. X is a halogen such as chlorine or bromineor an alkoxy. Where Z is silicon, then the terminating agent may be(R₁)aSiX_(b), where R₁ is an alkyl having from about 1 to about 20carbon atoms; a cycloalkyl having from about 3 to about 20 carbon atoms;an aryl having from about 6 to about 20 carbon atoms; or, an aralkylhaving from about 7 to about 20 carbon atoms. For example, R₁ mayinclude methyl, ethyl, n-butyl, neophyl, phenyl, cyclohexyl or the like.X is a halogen such as chlorine or bromine, "a" is an integer from 0 to3, and "b" is an integer from about 1 to 4; where a+b=4. Examples ofsuch terminating agents include silicon tetrachloride, (R₁)₃ SiCl, (R₁)₂SiCl₂, and R₁ SiCl₃. Preferably, the terminating agent is devoid of anyalkoxysilane (-Si(OR₁)_(x)) groups.

Examples of additional terminating agents include water, steam, analcohol such as isopropanol, carbodiimides, N-methylpyrrolidine, cyclicamides, cyclic ureas, isocyanates, Schiff bases, 4,4'-bis(diethylamino)benzophenone, and the like.

The terminating agent is added to the reaction vessel, and the vessel isagitated for about 1 to about 1000 minutes. As a result, an elastomer isproduced having an even greater affinity for silica compoundingmaterials, and hence, even further reduced hysteresis. Additionalexamples of terminating agents include those found in U.S. Pat. No.4,616,069 which is herein incorporated by reference. It is to beunderstood that practice of the present invention is not limited solelyto these terminators in as much as other compounds that are reactivewith the polymer bound lithium moiety can be selected to provide adesired functional group.

Quenching is usually conducted by stirring the polymer and quenchingagent for about 0.05 to about 2 hours at temperatures of from about 30°to 120° C. to ensure complete reaction. Polymers terminated with afunctional group as discussed hereinabove, are subsequently quenchedwith alcohol or other quenching agent as described hereinabove.

Lastly, the solvent is removed from the polymer by conventionaltechniques such as drum drying, extruder drying, vacuum drying or thelike, which may be combined with coagulation with water, alcohol orsteam, thermal desolventization, or any other suitable method. Ifcoagulation with water or steam is used, oven drying may be desirable.

The polymers of the present invention contain a functional group at boththe head of the polymer chain and at the terminal end of the chain.These functional groups have an affinity for silica. Such compoundingresults in products exhibiting reduced hysteresis, which means a producthaving increased rebound, decreased rolling resistance and has lessenedheat build-up when subjected to mechanical stress. Products includingtires, power belts and the like are envisioned. Decreased rollingresistance is, of course, a useful property for pneumatic tires, bothradial as well as bias ply types and thus, the vulcanizable elastomericcompositions of the present invention can be utilized to formtreadstocks for such tires.

The polymers of the present invention can be utilized as 100 parts ofthe rubber in the treadstock compound or, they can be blended with anyconventionally employed treadstock rubber which includes natural rubber,synthetic rubber and blends thereof. Such rubbers are well known tothose skilled in the art and include synthetic polyisoprene rubber,styrene/butadiene rubber (SBR), polybutadiene, butyl rubber, neoprene,ethylene/propylene rubber, ethylene/propylene/diene rubber (EPDM),acrylonitrile/butadiene rubber (NBR), silicone rubber, thefluoroelastomers, ethylene acrylic rubber, ethylene vinyl acetatecopolymer (EVA), epichlorohydrin rubbers, chlorinated polyethylenerubbers, chlorosulfonated polyethylene rubbers, hydrogenated nitrilerubber, tetrafluoroethylene/propylene rubber and the like. When thepolymers of the present invention are blended with conventional rubbers,the amounts can vary widely in a range comprising about 10 to about 99percent by weight of the total rubber. It is to be appreciated that theminimum amount will depend primarily upon the degree of reducedhysteresis that is desired.

According to the present invention, amorphous silica (silicon dioxide)is utilized as a filler for the elastomer. Silicas are generally classedas wet-process, hydrated silicas because they are produced by a chemicalreaction in water, from which they are precipitated as ultrafine,spherical particles. Silica filler has found limited use in the past,however, because it is acidic in nature and interferes with the cureprocess. Compensation for this phenomenon has been required.

These primary particles strongly associate into aggregates, which inturn combine less strongly into agglomerates. The surface area, asmeasured by the BET method gives the best measure of the reinforcingcharacter of different silicas. For silicas of interest for the presentinvention, the surface area should be about 32 to about 400 m² /g, withthe range of about 100 to about 250 m² /g being preferred, and the rangeof about 150 to about 220 m² /g being most preferred. The pH of thesilica filler is generally about 5.5 to about 7 or slightly over,preferably about 5.5 to about 6.8.

Silica can be employed in the amount of about 1 part to about 100 partsper 100 parts of polymer (phr), preferably in an amount from about 5 toabove 80 phr. The useful upper range is limited by the high viscosityimparted by fillers of this type. Some of the commercially availablesilicas which may be used include: Hi-Sil® 190, Hi-Sil® 215, and Hi-Sil®233, produced by PPG Industries. Also, a number of useful commercialgrades of different silicas are available from De Gussa Corporation,Rhone Poulenc, and J. M. Huber Corporation.

The polymers may also be compounded with all forms of carbon black inamounts ranging from about 0 to about 50 parts by weight, per 100 partsof rubber (phr), with less than about 5 phr being preferred in someinstances. The carbon blacks may include any of the commonly available,commercially-produced carbon blacks but those having a surface area(EMSA) of at least 20 m² /gram and more preferably at least 35 m² /gramup to 200 m² gram or higher are preferred. Surface area values used inthis application are those determined by ASTM test D-1765 using thecetyltrimethyl-anmnonium bromide (CTAB) technique. Among the usefulcarbon blacks are furnace black, channel blacks and lamp blacks. Morespecifically, examples of the carbon blacks include super abrasionfurnace (SAF) blacks, high abrasion furnace (HAF) blacks, fast extrusionfurnace (FEF) blacks, fine furnace (FF) blacks, intermediate superabrasion furnace (ISAF) blacks, semi-reinforcing furnace (SRF) blacks,medium processing channel blacks, hard processing channel blacks andconducting channel blacks. Other carbon blacks which may be utilizedinclude acetylene blacks. Mixtures of two or more of the above blackscan be used in preparing the carbon black products of the invention.Typical values for surface areas of usable carbon blacks are summarizedin the TABLE I hereinbelow.

                  TABLE I    ______________________________________    Carbon Blacks    ASTM Designation                   Surface Area (m.sup.2 /g)    (D-1765-82a)   (D-3765)    ______________________________________    N-110          126    N-220          111    N-339          95    N-330          83    N-351          74    N-550          42    N-660          35    ______________________________________

The carbon blacks utilized in the preparation of the rubber compounds ofthe invention may be in pelletized form or an unpelletized flocculentmass. Preferably, for more uniform mixing, unpelletized carbon black ispreferred.

The reinforced rubber compounds can be cured in a conventional mannerwith known vulcanizing agents at about 0.2 to about 5 phr. For example,sulfur or peroxide-based curing systems may be employed. For a generaldisclosure of suitable vulcanizing agents one can refer to Kirk-Othmer,Encyclopedia of Chemical Technology, 3rd ed., Wiley Interscience, N.Y.1982, Vol. 20, pp. 365-468, particularly "Vulcanization Agents andAuxiliary Materials" pp. 390-402. Vulcanizing agents can be used aloneor in combination.

Vulcanizable elastomeric compositions of the invention can be preparedby compounding or mixing the functionalized polymers herein with carbonblack, silica, and other conventional rubber additives including forexample, fillers, plasticizers, antioxidants, curing agents and the likeusing standard rubber mixing equipment and procedures. Such elastomericcompositions when vulcanized using conventional rubber vulcanizationconditions have reduced hysteresis properties and are particularlyadapted for use as tread rubbers for tires having reduced rollingresistance.

GENERAL EXPERIMENTAL

In order to demonstrate the preparation and properties of elastomericcompositions prepared according to the present invention, several dieneelastomers were prepared according to the above disclosure. Amineinitiators were used to form styrene butadiene rubber (SBR) formulationsused in the preparation of silica filled and control samples. Further,amino group producing terminators were utilized to terminate thereaction in examples according to the invention, but not in certaincontrol experiments. As noted above, various techniques known in the artfor carrying out polymerizations may be used with the inventive amineinitiator/amino group producing terminator-silica filler combination,without departing from the scope of the present invention.

The polymerizations were carried out in jacketed stainless steelpressure reactors under a blanket of dry nitrogen. The pressure in thereactors was maintained between 40 and 70 psi during the course of thepolymerization. In all cases, the reactors were first charged with a24-26 wt % solution of butadiene in hexane. Following the addition ofbutadiene, a 33 wt % solution of styrene in hexane was added. Themonomer blend was agitated while the modifier and initiator componentswere added. The polymerizations were initiated at or near roomtemperature. The temperature of the polymerizations was regulated suchthat the highest temperature recorded during the polymerization wasbelow 135° F.

The copolymers were stabilized with tertiary-butyl-p-cresol as anantioxidant. The copolymers were isolated by adding the cements to anexcess of isopropanol followed by drum drying. These copolymers werecompounded into one of four formulations. The main reinforcing filler inall of these formulations was silica. The formulations are described inTable II. The formula used for each copolymer are indicated in thetables of physical properties (Tables IIIC, IVC, and VC).

                  TABLE II    ______________________________________    Cure Formulations for Experimental Compositions                 A    B         C      D    ______________________________________    Copolymer      100    100       100  75    Natural Rubber --     --        --   25    Silica         40     40        40   50    Wax            --     --        --   1    N339 HS-HAF    8      8         8    --    Antioxidant    1      1         1    0.95    Aromatic Oil   --     --        --   15    Dicyclohexylamine                   --     1         1    --    Si69           --     1         1    --    Stearic Acid   2      2         4    1.5    Sulfur cure package A                   4.3    --        --   --    Sulfur cure package B                   --     3.8       3.8  4.5    Zinc Oxide     3      3         3    3    ______________________________________

EXAMPLES 1-6

For polymerizations conducted according to the above GeneralExperimental method in which only modifier and either butyllithium or3-dimethylaminopropyllithium were utilized, the modifier was added firstfollowed by the initiator. For polymerizations involving lithium imidesderived from secondary amines such as diethylamine, or dibutylamine, themodifier was added first, butyllithium (BuLi) was added second and thesecondary amine was added last. The BuLi and secondary amine reacted insitu to form the lithium imide initiator. The exact amounts of monomer,initiator and modifier used in these polymerizations are reported inTables IIIA, IVA & VA, and VIA. The initial temperatures and maximumtemperatures observed during these polymerizations are also included inthese Tables.

                                      TABLE IIIA    __________________________________________________________________________    Example No.  1   2   3   4   5   6    __________________________________________________________________________    BuLi (mmol)  24.6                     11.5                         11.5                             20.5                                 9.7 10.8    Et.sub.2 NH (mmol)   9.3         9.3    Bu.sub.2 NH (mmol)                     11.1                         9.4    Randomizer (mmol)                 6.9 3.1 3.1 5.7 2.8 3.2    Butadiene (grams)                 2183                     937 937 2141                                 945 945    Styrene (grams)                 767 365 365 748 367 367    Time (hours) 3.5 2.5 2   3   3.5 2    Temp. (° F.) (start/max)                 70/135                     60/138                         77/115                             65/132                                 75/135                                     70/125    % Styrene    26  28  28  26  28  28    wt. % monomer                 25.4                     25.3                         26.1                             25.4                                 26.3                                     26.3    Batch Size (lbs.)                 25  11.35                         11  25  11  11    Reactor Size (gal.)                 5   2   2   5   2   2    __________________________________________________________________________     BuLi: Butyl Lithium     Bu.sub.2 NH: Dibutylamine     Et.sub.2 NH: Diethylamine

                                      TABLE IIIB    __________________________________________________________________________    Example No.  1   2   3   4   5   6    __________________________________________________________________________    Initiator    BuLi                     Bu.sub.2 NLi                         Et.sub.2 NLi                             BuLi                                 Bu.sub.2 NLi                                     Et.sub.2 NLi    % solids (theory)                 25.4                     25.3                         26.1                             25.4                                 26.3                                     26.3    % solids (found)                 24.8                     21.0                         22.7                             23.5                                 24.9                                     24.1    Mn (×10.sup.-3 g/mol, theory)                 120 125 125 140 140 125    Mn (×10.sup.-3 g/mol)                 114 88  95  163 137 134    Mw (×10.sup.-3 g/mol)                 122 127 122 178 181 174    PDI          1.07                     1.44                         1.28                             1.09                                 1.32                                     1.30    % Styrene    27  27  29  25  29  29    % vinyl      52  55  55  52  52  44    Tg (° C.)                 -36 -35 -30 -37 -34 -42    __________________________________________________________________________     BuLi: Butyl Lithium     Bu.sub.2 NLi: Lithium Dibutylamide     Et.sub.2 NLi: Lithium Diethylamide     PDI = Poly Dispersity Index (Mw/Mn)

                                      TABLE IIIC    __________________________________________________________________________    Example No. 1    2    3    4    5    6    __________________________________________________________________________    Cure Formulation                B    B    B    B    B    B    Initiator   BuLi Bu.sub.2 NLi                          Et.sub.2 NLi                               BuLi Bu.sub.2 NLi                                         Et.sub.2 NLi    ML.sub.(1+4)                50   72   76   87   113  111    ML          4    6    `3   6    10   10    MH          45   45   43   48   50   50    Hardness (RT)                75   73        73   73   73    % Rebound (65° C.)                58   60        64   63   67    Ring Tear 340° F. (lb/in)                143  144       126  155  204    ΔG'(65° C., MPa)                4.3  2.3  1.4  4.2  2.5  2.9    tan δ at 7% strain (65° C.)                0.172                     0.127                          0.096                               0.139                                    0.111                                         0.131    200% Modules (psi)                1082 1158 1284 1174 1287 1267    Stress at max (psi)                1993 1877 1986 2028 2164 2286    % Strain at Max                336  299  289  314  302  324    __________________________________________________________________________     BuLi: Butyl Lithium     Bu.sub.2 NLi: Lithium Dibutylamide     Et.sub.2 NLi: Lithium Diethylamide

EXAMPLES 7-12

A number of polymerizations were terminated with N-ethylpyrrolidinone,4,4'-bis(diethylamino)benzophenone or dimethylimidizolidinone. Thepolymerization conditions for these polymers are recorded in Table IVA &VA. Prior to terminating the live polymer cements with theseterminators, a portion of the cement was removed and isolated. Theterminating agent was then added to the remainder of the batch. Theamount of cement removed prior to the addition of the terminators isindicated in Table IVA & VA.

                                      TABLES IVA and VA    __________________________________________________________________________    Example No.     7   8   9   10  11  12    __________________________________________________________________________    BuLi (mmol)     12  11.4                            10.8                                10.5                                    10.5                                        10.8    Et.sub.2 NLi (mmol)                    9.6 9.6 10.5    Bu.sub.2 NLi (mmol)         10.8                                    10.8                                        10.5    Randomizer (mmol)                    3.1 3.1 3.1 3   3   3.1    Butadiene (grams)                    938 938 945 911 911 945    Styrene (grams) 365 365 367 354 354 367    wt. % monomer   26.1                        26.1                            26.3                                25.4                                    25.4                                        26.3    Time (hrs)      3   2   3   2.5 5   2.5    Temp (° F.) (start/max)                    48/125                        77/115                            80/120                                75/120                                    90/115                                        75/135    Total Charge (lbs)                    11  11  11  11  11  11    Amount removed prior to termination                    5   5   5   5   5   5    (lbs)    DMI (mmol)      12.4        6.38    N-Ethylpyrrolidinone (mmol)                            6.11        6.3    (Et.sub.2 N).sub.2 BP (mmol)                        6.3         6.3    __________________________________________________________________________     BuLi: Butyl Lithium     Bu.sub.2 NLi: Lithium Dibutylamide     Et.sub.2 NLi: Lithium Diethylamide     (Et.sub.2 N).sub.2 BP: 4,4Bis(diethylamino)benzophenone     DMI: Dimethylimidizolidinone

                                      TABLE IVB    __________________________________________________________________________    Example No.               7A  7B  8A  8B   9A  9B    __________________________________________________________________________    Initiator  Et.sub.2 NLi                   Et.sub.2 NLi                       Et.sub.2 NLi                           Et.sub.2 NLi                                Et.sub.2 NLi                                    Et.sub.2 NLi    Terminator     DMI     (Et.sub.2 N).sub.2 BP                                    N--Et-Pyrol    % solids (theory)               26.1    26.1     26.3    % solids (found)               24.0    22.7     25.1    Mn (×10.sup.-3 g/mol, theory)               125     125      125    Mn (×10.sup.-3 g/mol)               101 66  95  94   130 129    Mw (×10.sup.-3 g/mol)               144 108 122 119  168 169    PDI        1.43                   1.63                       1.28                           1.27 1.29                                    1.31    % Styrene  29  29  29  30   29  29    % vinyl    48  48  55  55   53  51    Tg (° C.)               -44 -44 -30 -28  -34 -34    __________________________________________________________________________     Et.sub.2 NLi: Lithium Diethylamide     DMI: Dimethylimidizolidinone     (Et.sub.2 N).sub.2 BP: 4,4Bis(diethylamino)benzophenone     N--EtPyrol: NEthyl-Pyrollidonone     PDI: Poly Dispersity Index (Mw/Mn)

                                      TABLE IVC    __________________________________________________________________________    Example No. 7A  7B   8A   8B    9A   9B    __________________________________________________________________________    Cure Formulation                A   A    A    A     A    A    Initiators  Et.sub.2 NLi                    Et.sub.2 NLi                         Et.sub.2 NLi                              Et.sub.2 NLi                                    Et.sub.2 NLi                                         Et.sub.2 NLi    Terminator      DMI       (Et.sub.2 N).sub.2 BP                                         N--Et-Pyrol    ML.sub.(1+4)                158 174  136  150   178  186    Hardness (RT)                74  75   76   73    79   77    % Rebound (65° C.)                63  62   65   66    65   68    ΔG'(65° C., MPa)                3.7 1.5  3.2  2.1   4.0  3.5    tan δ at 7% strain (65° C.)                0.105                    0.080                         0.096                              0.090 0.101                                         0.092    200% Modulus (psi)                679 995  831  1127  1162 1210    Stress at Max (psi)                959 1774 1492 1564  1788 1873    % Strain at Max                285 336  345  277   306  305    __________________________________________________________________________     Et.sub.2 NLi: Lithium Diethylamide     DMI: Dimethylimidizolidinone     (Et.sub.2 N).sub.2 BP: 4,4Bis(diethylamino)benzophenone     N--EtPyrol: NEthyl-Pyrollidinone

                                      TABLE VB    __________________________________________________________________________    Example No.               10A 10B 11A 11B  12A 12B    __________________________________________________________________________    Initiator  Bu.sub.2 NLi                   Bu.sub.2 NLi                       Bu.sub.2 NLi                           Bu.sub.2 NLi                                Bu.sub.2 NLi                                    Bu.sub.2 NLi    Terminator     DMI     (Et.sub.2 N).sub.2 BP                                    N--Et-Pyrol    % solids (theory)               25.4    25.4     26.3    % solids (found)               23.6    24.2     25.2    Mn (×10.sup.-3 g/mol, theory)               125     125      125    Mn (×10.sup.-3 g/mol)               107 94  100 99   132 128    Mw (×10.sup.-3 g/mol)               141 133 109 106  199 307    PDI        1.32                   1.41                       1.09                           1.07 1.51                                    2.40    % Styrene  29  29  30  30   30  30    % vinyl    49  50  52  50   52  54    Tg (° C.)               -35 -35 -31 -31  -33 -34    __________________________________________________________________________     Bu.sub.2 NLi: Lithium Dibutylamide     DMI: Dimethylimidizolidinone     (Et.sub.2 N).sub.2 BP: 4,4Bis(diethylamino)benzophenone     N--EtPyrol: NEthyl-Pyrollidinone     PDI: Polymer Dispersity Index (Mw/Mn)

                                      TABLE VC    __________________________________________________________________________    Example No. 10A  10B  11A  11B  12A  12B    __________________________________________________________________________    Cure Formulation                C    C    A    A    A    A    Initiator   Bu.sub.2 NLi                     Bu.sub.2 NLi                          Bu.sub.2 NLi                               Bu.sub.2 NLi                                    Bu.sub.2 NLi                                         Bu.sub.2 NLi    Terminator       DMI       (Et.sub.2 N).sub.2 BP                                         N--Et-Pyrol    ML.sub.(1+4)                73   117  111  125  171  190    Hardness (RT)                67   66   82   80   80   76    % Rebound (65° C.)                67   74   58   64   61   65    ΔG'(65° C., MPa)                1.2  0.4  5.3  3.9  4.6  2.1    tan δ at 7% strain (65° C.,)                0.102                     0.069                          0.124                               0.101                                    0.103                                         0.077    200% Modulus (psi)                1088 1149 1080 1113 1114 1545    Stress at Max (psi)                2319 2414 1465 1574 1718 2337    % Strain at Max                360  349  273  282  303  282    __________________________________________________________________________     Bu.sub.2 NLi: Lithium Dibutylamide     DMI: Dimethylimidizolidinone     (Et.sub.2 N).sub.2 BP: 4,4Bis(diethylamino)benzophenone     N--EtPyrol: NEthyl-Pyrollidinone

                                      TABLE VIA    __________________________________________________________________________    Example No.  13  14  15  16  17  18    __________________________________________________________________________    BuLi (mmol)  4.78    25.2    14.7    Me.sub.2 NPrLi (mmol)                     5.46    4.78    3.95    Randomizer (mmol)                 1.19                     1.36                         6.56                             1.19                                 3.67                                     0.99    Butadiene (grams)                 430 430 2148                             430 1323                                     430    Styrene (grams)                 143 143 755 143 441 143    wt. % monomer                 25.3                     25.3                         25.6                             25.3                                 25.9                                     25.3    Time (hrs)   2   3   2.5 2.5 3   4    Temp. (° F.) (start/max)                 85/130                     80/120                         76/125                             85/125                                 80/125                                     85/125    % styrene    25  25  26  25  25  25    Reactor Size (gal)                 1   1   5   1   5   1    Batch size (lbs)                 5   5   25  5   15  5    __________________________________________________________________________     BuLi: Butyl Lithium     Me.sub.2 NPrLi: 3Dimethylaminopropyllithium

                                      TABLE VIB    __________________________________________________________________________    Example No.  13  14  15  16  17  18    __________________________________________________________________________    Initiator    BuLi                     Me.sub.2 N                         BuLi                             Me.sub.2 N                                 BuLi                                     Me.sub.2 N                     PrLi    PrLi    PrLi    % solids (theory)                 25.3                     25.3                         25.6                             25.3                                 25.9                                     25.3    % solids (found)     24.0                             24.0    ML.sub.(1+4) 14  16  18  22  41  33    Mn (×10.sup.-3 g/mol, theory)                 120 105 115 120 120 145    Mn (×10.sup.-3 g/mol)                 104 103 130 121 121 131    Mw (×10.sup.-3 g/mol)                 110 105 139 128 131 139    PDI          1.06                     1.06                         1.07                             1.06                                 1.08                                     1.06    % Styrene    26  26  27  27  26  28    % vinyl      44  52  53  49  33  48    Tg (° C.)                 -44 -35 -34 -39 -58 -38    __________________________________________________________________________     BuLi: Butyl Lithium     Me.sub.2 NPrLi: 3Dimethylaminopropyllithium

                                      TABLE VIC    __________________________________________________________________________    Example No. 13   14   15   16   17   18    __________________________________________________________________________    Initiator   BuLi Me.sub.2 N                          BuLi Me.sub.2 N                                    BuLi Me.sub.2 N                     PrLi      PrLi      PrLi    Cure Formulation                D    D    D    D    D    D    ML.sub.(1+4)                90   88   86   93   92   99    tan δ at 7% strain (65° C.)                0.122                     0.105                          0.107                               0.099                                    0.129                                         0.094    % Rebound (65° C.)                62   71   62   71   63   72    ΔG'(65° C., MPa)                4.9  2.5  4.6  2.9  4.4  2.7    300% Modulus (psi)                753  1001 814  1020 736  990    % strain at Max                536  458  497  452  580  494    __________________________________________________________________________     BuLi: Butyl Lithium     Me.sub.2 NPrLi: 3Dimethylaminopropyllithium

As shown in Tables III through VI, Examples 2, 3, 5-12, 14, 16, and 18demonstrate embodiments of the present invention, while Examples 1, 4,13, 15, and 17 provide control comparisons of the prior art. It canreadily be recognized that the present invention, involving thepreparation of silica-filled, particularly amorphous silica-filled,elastomeric compositions utilizing both amine initiators and amino groupproducing terminating agents, results in a marked reduction ofhysteresis in the cured compounds. This is demonstrated in all of theinventive Examples, by the ΔG' values.

It has been previously shown that not all lithium amines used asinitiators produce elastomers with reduced hysteresis for carbon blackfilled rubber stocks. Unexpectedly, however, according to thisinvention, some of the lithium amine initiators which do not provideelastomers of improved (decreased) hysteresis for carbon black filledrubber stocks, do provide such improved hysteresis in silica filledrubber stocks. It can be concluded, therefore, that the interactionbetween the polymer amine functionalities and the silica fillers aredifferent from the interactions between the polymer aminefunctionalities and the carbon black fillers.

It should be appreciated that the present invention is not limited tothe specific embodiments described above, but includes variations,modifications and equivalent embodiments defined by the followingclaims.

We claim:
 1. A process for the production of diene-based elastomericcompositions having reduced hysteresis properties when compounded withsilica filler and vulcanized, the process comprising:mixing a dienemonomer and optionally a monovinyl aromatic monomer or a triene with alithium amine initiator compound optionally in the presence of amodifier, wherein the lithium amine initiator compound is selected fromthe group consisting of compounds of the formulas R'₂ N-Li and R'₂N-R"-Li, wherein each R' is the same or different and is a C₁₋₁₂hydrocarbyl group and wherein R" is a divalent hydrocarbyl group of 2 to20 carbons and the lithium atom is not bonded to a carbon which isdirectly bonded to the amine nitrogen; effecting polymerizationconditions; terminating polymerization with an amino group-producingterminating agent to form an amine functionalized diene elastomer;compounding the functionalized diene elastomer with an amorphous silicafiller, and a vulcanization agent; and, effecting vulcanization of thesilica filled, functionalized diene filled elastomeric compound.
 2. Aprocess as in claim 1 wherein each R' is a C₁₋₁₂ alkyl group.
 3. Aprocess as in claim 1 wherein R" is a C₃₋₈ divalent alkylene wherein thenitrogen and lithium atoms are separated by at least 3 carbon atoms. 4.A process as in claim 1 wherein the lithium amine initiator is selectedfrom the group consisting of 3-dimethylaminopropyllithium, and thelithium imides of dimethylamine, diethylamine, dipropylamine,dibutylamine, and mixtures thereof.
 5. A process as in claim 1, whereinsaid terminating agent is devoid of an alkoxysilane group.
 6. A processas in claim 1 wherein the amino group producing terminator is selectedfrom the group consisting of4,4'-bis(dialkylamino)benzophenone;N,N-dialkylamino-benzaldehyde;1,3-dialkyl-2-imidazolidinones; 1-alkyl substituted pyrrolidinones;1-aryl substituted pyrrolidinones; dialkyl- anddicycloalkyl-carbodiimides having from about 5 to about 20 carbon atoms;##STR2## wherein each R₂ is the same or different and is an alkyl,cycloalkyl ar aryl, having from 1 to about 12 carbon atoms;R₃ is analkyl, phenyl, alkylphenyl or dialkylaminophenyl, having from 1 to about20 carbon atoms; Each R₄ is the same or different, and is an alkyl orcycloalkyl having from 1 to about 12 carbon atoms; and wherein two ofthe R₄ groups may together form a cyclic group; R₅ is alkyl, phenyl,alkylphenyl or dialkylaminophenyl, having from 1 to about 20 carbonatoms.
 7. A process as in claim 1 wherein the step of terminatingemploys an additional terminator having the structural formula, (R₁)_(a)ZX_(b) ; wherein Z is silicon; R₁ is an alkyl having from 1 to about 20carbon atoms; a cycloalkyl having from about 3 to about 20carbon atoms;an aryl having from about 6 to about 20 carbon atoms; or, an aralkylhaving from about 7 to about 20 carbon atoms;X is a halogen, a is from 0to 3, and b is from 1 to 4; where a+b=4.
 8. A process as in claim 1wherein the step of terminating employs an additional terminator havingthe formula (R₁)₃ SnX, wherein R₁, is an alkyl having from 1 to about 20carbons atoms; a cycloalkyl having from about 3 to about 20 carbonatoms; an aryl having from about 6 to about 20 carbon atoms; or anaralkyl having from about 7 to about 20 carbon atoms; and X is a halogenor an alkoxy.
 9. A process as in claim 6 including terminatingpolymerization with an additional terminator selected from the groupconsisting of water, steam, an alcohol, carbodiimides,N-methylpyrrolidine, cyclic amides, cyclic ureas, isocyanates, Schiffbases, 4,4'-bis(diethylamino) benzophenone, and mixtures thereof.
 10. Aprocess as in claim 7 wherein each R₁ is the same or different and ismethyl, ethyl, butyl, octyl, cyclohexyl, 3-phenyl-1-propyl, isobutyl,and mixtures thereof.
 11. A process as in claim 1 wherein the silicafiller has a surface area of about 32 to about 400 m2/g.
 12. A processas in claim 1 wherein the silica filler has a pH in the range of about5.5 to about
 7. 13. A process as in claim 1 including compounding theamine functionalized diene elastomer with carbon black.
 14. Avulcanizable silica-filled compound comprising a diene elastomercontaining a lithium amine initiator-derived functionality and afunctionality derived from an amino group-producing terminator, anamorphous silica filler, and a vulcanization agent, wherein the lithiumamine initiator-derived functionality is a residue of a lithium amineinitiator derived from a reaction of a secondary amine with ahydrocarbyl lithium and of the formula R'₂ N-li, wherein each R' is thesame or different and is a C₁₋₁₂ hydrocarbyl group.
 15. The vulcanizablesilica-filled compound of claim 14 wherein the elastomer is selectedfrom the group consisting of conjugated diene polymers and copolymersthereof prepared from monomers selected from the group consisting ofmonovinyl aromatic monomers and trienes.
 16. The vulcanizablesilica-filled compound of claim 14 wherein each R' is a C₁₋₁₂ alkylgroup.
 17. The vulcanizable silica-filled compound of claim 14 whereinthe lithium amine initiator functionality is selected from the groupconsisting of the lithium imides of dimethylamine, diethylamine,dipropylamine, dibutylamine, and mixtures thereof.
 18. The vulcanizablesilica-filled compound of claim 14 wherein the terminator functionalityis devoid of an alkoxysilane functionality.
 19. The vulcanizablesilica-filled compound of claim 14 wherein the terminator functionalityis an amino containing functionality and the amino containingfunctionality is a residue of an amino group producing terminatorselected from the group consisting of 4,4'-bis(dialkylamino)benzophenone;N,N-dialkylamino-benzaldehyde;1,3-dialkyl-2-imidazolidinones;1-alkyl substituted pyrrolidinones; 1-aryl substituted pyrrolidinones;dialkyl- and dicycloalkyl-carbodiimides having from about 5 to about 20carbon atoms; ##STR3## wherein each R₂ is the same or different and isan alkyl, cycloalkyl or aryl, having from 1 to about 12 carbon atoms;R₃is an alkyl, phenyl, alkylphenyl or dialkylaminophenyl, having from 1 toabout 20 carbon atoms; Each R₄ is the same or different, and is an alkylor cycloalkyl having from 1 to about 12 carbon atoms; and wherein two ofthe R₄ groups may together form a cyclic group; R₅ is alkyl, phenyl,alkylphenyl or dialkylaminophenyl, having from 1 to about 20 carbonatoms.
 20. The vulcanizable silica-filled compound of claim 14 whereinthe terminator functionality further includes a residue of a terminatorhaving the structural formula (R₁)_(a) ZX_(b) ;wherein Z is silicon; R₁is an alkyl having from 1 to about 20 carbon atoms; a cycloalkyl havingfrom about 3 to about 20 carbon atoms; an aryl having from about 6 toabout 20 carbon atoms; or, an aralkyl having from about 7 to about 20carbon atoms; X is a halogen, a is from 0 to 3, and b is from 1 to 4;where a+b=4.
 21. The vulcanizable silica-filled compound of claim 14wherein the terminator functionality further includes a residue of aterminator having the formula (R₁)SnX, wherein R₁, is an alkyl havingfrom 1 to about 20 carbons atoms; a cycloalkyl having from about 3 toabout 20 carbon atoms; an aryl having from about 6 to about 20 carbonatoms; or an aralkyl having from about 7 to about 20 carbon atoms; and Xis a halogen or an alkoxy.
 22. The vulcanizable silica-filled compoundof claim 14 wherein the silica filler has a surface area of about 32 toabout 400 m2/g.
 23. The vulcanizable silica-filled compound of claim 14wherein the silica filler has a pH in the range of about 5.5 to about 7.24. The vulcanizable silica-filled compound of claim 14 furthercontaining a carbon black filler.
 25. The vulcanizable silica-filledcompound of claim 14 further containing a natural rubber.
 26. Thevulcanizable silica-filled compound of claim 14 wherein silica ispresent in an amount of about 1 phr to about 100 phr.
 27. A pneumatictire having decreased rolling resistance comprising tread stockvulcanized from the vulcanizable silica-filled compound of claim
 14. 28.The vulcanizable silica-filled compound comprising a diene elastomercontaining a lithium amine-derived functionality and a functionalityderived from an amino group-producing terminator, an amorphous silicafiller, and a vulcanization agent, wherein the lithium amine-derivedfunctionality is a residue of a lithium-hydrocarbon substituted tertiaryamine of the formula R'₂ N-R"-Li, wherein each R' is the same ordifferent and is a C₁₋₁₂ hydrocarbyl group, and wherein R" is a divalenthydrocarbyl group of 20 to 20 carbons and the lithium atom is not bondedto a carbon which is directly bonded to the amine nitrogen.
 29. Thevulcanizable silica-filled compound of claim 28 wherein the elastomer isselected from the group consisting of conjugated diene polymers andcopolymers thereof prepared from monomers selected from the groupconsisting of monovinyl aromatic monomers and trienes.
 30. Thevulcanizable silica-filled compound of claim 28 wherein each R' is aC₁₋₁₂ alkyl group and R" is a C₃₋₈ divalent alkylene wherein thenitrogen and lithium atoms are separated by at least 3 carbon atoms. 31.The vulcanizable silica-filled compound of claim 28 wherein the lithiumamine initiator functionality is 3-dimethylaminopropyllithium.
 32. Thevulcanizable silica-filled compound of claim 28 wherein the terminatorfunctionality is devoid of an alkoxysilane functionality.
 33. Thevulcanizable silica-filled compound of claim 28 wherein the terminatorfunctionality is an amino containing functionality and the aminocontaining functionality is a residue of an amino group producingterminator selected from the group consisting of4,4'-bis(dialkylamino)benzophenone; N,N-dialkylamino-benzaldehyde;1,3-dialkyl-2-imidazolidinones; 1-alkyl substituted pyrrolidinones;1-aryl substituted pyrrolidinones; dialkyl- anddicycloalkyl-carbodiimides having from about 5 to about 20 carbon atoms;##STR4## wherein each R₂ is the same or different and is an alkyl,cycloalkyl or aryl, having from 1 to about 12 carbon atoms;R₃ is analkyl, phenyl, alkylphenyl or dialkylaminophenyl, having from 1 to about20 carbon atoms; Each R₄ is the same or different, and is an alkyl orcycloalkyl having from 1 to about 12 carbon atoms; and wherein two ofthe R₄ groups may together form a cyclic group; R₅ is alkyl, phenyl,alkylphenyl or dialkylaminophenyl, having 1 to about 20 carbon atoms.34. The vulcanizable silica-filled compound of claim 28 wherein theterminator functionality further includes a residue of a terminatorhaving the structural formula (R₁)_(a) ZX_(b) ;wherein Z is silicon; R₁is an alkyl having from 1 to about 20 carbon atoms; a cycloalkyl havingfrom about 3 to about 20 carbon atoms; an aryl having from about 6 toabout 20 carbon atoms; or, an aralkyl having from about 7 to about 20carbon atoms; X is a halogen, a is from 0 to 3, and b is from 1 to 4;where a+b=4.
 35. The vulcanizable silica-filled compound of claim 28wherein the terminator functionality further includes a residue of aterminator having the formula (R₁)₃ SnX, wherein R₁, is an alkyl havingfrom 1 to about 20 carbons atoms; a cycloalkyl having from about 3 toabout 20 carbon atoms; and aryl having from about 6 to about 20 carbonatoms; or an aralkyl having from about 7 to about 20 carbon atoms; and Xis a halogen or an alkoxy.
 36. The vulcanizable silica-filled compoundof claim 28 wherein the silica filler has a surface area of about 32 toabout 400 m2/g.
 37. The vulcanizable silica-filled compound of claim 28wherein the silica filler has a pH in the range of about 5.5 to about 7.38. The vulcanizable silica-filled compound of claim 28 furthercontaining a carbon black filler.
 39. The vulcanizable silica-filledcompound of claim 28 further containing a natural rubber.
 40. Thevulcanizable silica-filled compound of claim 28 wherein silica ispresent in an amount of about 1 phr to about 100 phr.
 41. A pneumatictire having decreased rolling resistance comprising tread stockvulcanized from the vulcanizable silica-filled compound of claim 28.